Plasticating apparatus screw having grooves of varying angles and depths

ABSTRACT

A screw for a plasticating apparatus has one or more helical flights. A portion of the screw has a plurality of advancing grooves arranged in a noncontinuous helix cut in the screw. The advancing grooves are dimensioned to receive material therein as the material is conveyed through the barrel. The screw has a plurality of noncontinuous cross-cut grooves traversing one or more of the advancing grooves. The cross-cut grooves have a second helix angle greater than the first helix angle and less than ninety degrees; and/or one or more of the cross-cut grooves have a third helix angle of about ninety degrees.

CROSS REFERENCE TO RELATED APPLICATION

The instant application is a divisional application of U.S.Non-Provisional patent application Ser. No. 16/697,491, filed Nov. 27,2019, which is a divisional application of U.S. Non-Provisional patentapplication Ser. No. 15/091,802, filed Apr. 6, 2016, now U.S. Pat. No.10,532,490 and entitled “Plasticating Apparatus Screw Having Grooves ofVarying Angles and Depths,” the entirety of which is incorporated hereinby reference.

FIELD

This invention relates to a plasticating apparatus screw rotatablewithin a barrel to extrude molten resinous material. More particularly,this invention relates to a longitudinal portion of the screw designedto recirculate material for thorough mixing and melting via grooves ofvarious angles and having various depths and depth tapers.

BACKGROUND

A plasticating apparatus typically receives polymer or thermoplasticresin pellets, granules or powders, from an inlet port, then heats andworks the resin to convert it into a melted or molten state. The melt ormolten material is delivered under pressure through a restricted outletor discharge port to make the finished article. It is desirable that themolten material leaving the apparatus be completely melted andhomogeneously mixed, resulting in uniform temperature, viscosity, colorand composition.

A typical plasticating apparatus includes an elongated cylindricalbarrel, which is usually heated at various locations along its length.An axially supported and rotating screw extends longitudinally throughthe barrel. The screw is responsible for forwarding, melting,pressurizing and homogenizing the material as it passes from the inletport to the outlet port. The screw has a core with a helical flightthereon and the flight cooperates with the cylindrical inner surface ofthe barrel to define a helical channel for forward passage of the resinto the outlet port.

The typical plasticating screw has a plurality of sections along itslongitudinal axis with each section being designed for a particularfunction. Ordinarily, there is a feed section, a transition section, ametering section and a mixing section in series.

As disclosed in U.S. Pat. No. 6,498,399 and illustrated in FIG. 1 aplasticating screw 100 has a main channel defined by a helical flight113 disposed within and cooperating with an inner-wall of a heatedbarrel (not shown). As illustrated in FIG. 1, the prior art screw 100has a longitudinal portion with a plurality of staggered rows ofnoncontinuous advancing grooves 130 arranged in the main channelthereof. The axis of each row of advancing grooves 130 is substantiallyparallel to the helical axis of the adjacent helical flight 113 of thelongitudinal portion to promote flow in the direction indicated by thearrow 140. A noncontinuous helical channel is formed therein traversingin a reverse direction, compared with the direction of the helicalflight 113, the channel having a plurality of retracting grooves 137.While the objective of the retracting grooves 137 is to promote mixingof the polymer or thermoplastic resin pellets in the main channel, insome instances mixing is insufficient.

Based on the foregoing, it is the general object of this invention toprovide a screw configured for improved mixing of the polymer orthermoplastic resin pellets.

SUMMARY

The present invention resides in one aspect in a screw for aplasticating apparatus. The plasticating apparatus includes a barrelthat has an axial length extending between an inlet port and an outletport. The barrel has an inner wall. The screw has a longitudinal axisand is rotatably supported in the barrel for rotation about thelongitudinal axis. The screw has a core and one or more helical flightsextending along a length of the screw. The helical flight extends in afirst threaded direction and defines a first helix angle relative to areference line perpendicular to the longitudinal axis and defines afirst helical path oriented at the first helix angle which is less thanninety degrees. The helical flight defines a helical channel. The screwmay include a feed section cooperating with the inlet port, anintermediate melt section, and/or a metering section cooperating withsaid outlet port. A longitudinal portion of the screw (e.g., in the feedsection, the intermediate melt section, and/or the metering section) hasa plurality of advancing grooves formed therein. Each of the advancinggrooves has one or both ends closed. The advancing grooves are arrangedin a noncontinuous helix cut in the screw core in the helical channel ofthe screw. The plurality of advancing grooves are dimensioned to receivematerial therein as the material is conveyed through the helicalchannel, to the outlet port. The longitudinal portion further has aplurality of noncontinuous cross-cut grooves traversing one or more ofthe advancing grooves. One or more of the cross-cut grooves has a secondhelix angle (measured relative to a reference line perpendicular to thelongitudinal axis) greater than the first helix angle and less thanninety degrees; and/or one or more of another of the cross-cut grooveshas a third helix angle (measured relative to a reference lineperpendicular to the longitudinal axis) of about ninety degrees.

In one embodiment, each cross-cut groove passes through the helicalflight not more than two times so that the material can back flow andrecirculate within said longitudinal portion.

In one embodiment, one or more of the plurality of advancing groovesincludes an advancing groove depth taper; and/or one or more of theplurality of cross-cut grooves having a cross-cut groove depth taper.

The present invention also resides in another screw for a plasticatingapparatus. The plasticating apparatus includes a barrel that has anaxial length extending between an inlet port and an outlet port. Thebarrel has an inner wall. The screw has a longitudinal axis and isrotatably supported in the barrel for rotation about the longitudinalaxis. The screw has a core and one or more helical flights extendingalong a length of the screw. The helical flight defines a first helixangle relative to a reference line perpendicular to the longitudinalaxis and defines a first helical path oriented at the first helix anglewhich is less than ninety degrees. The helical flight defines a helicalchannel. The screw may include a feed section cooperating with the inletport, an intermediate melt section, and/or a metering sectioncooperating with said outlet port. A longitudinal portion of the screw(e.g., in the feed section, the intermediate melt section, and/or themetering section) has a plurality of advancing grooves formed therein.Each of the advancing grooves has one or both ends closed. The advancinggrooves are arranged in a noncontinuous helix cut in the screw core inthe helical channel of the screw. The plurality of advancing grooves aredimensioned to receive material therein as the material is conveyedthrough the helical channel, to the outlet port. The longitudinalportion further has a plurality of noncontinuous cross-cut groovestraversing several advancing grooves. One or more of the plurality ofadvancing grooves has an advancing groove depth taper; and/or one ormore of the plurality of cross-cut grooves has a cross-cut groove depthtaper.

The present invention also resides in yet another screw for aplasticating apparatus. The plasticating apparatus includes a barrelthat has an axial length extending between an inlet port and an outletport. The barrel has an inner wall. The screw has a longitudinal axisand is rotatably supported in the barrel for rotation about thelongitudinal axis. The screw has a core and one or more helical flightsextending along a length of the screw. The helical flight defines afirst helix angle relative to a reference line perpendicular to thelongitudinal axis and defines a first helical path oriented at the firsthelix angle which is less than ninety degrees. The helical flightdefines a helical channel. The screw may include a feed sectioncooperating with the inlet port, an intermediate melt section, and/or ametering section cooperating with said outlet port. A longitudinalportion of the screw (e.g., in the feed section, the intermediate meltsection, and/or the metering section) has a plurality of advancinggrooves formed therein. Each of the advancing grooves has one or bothends closed. The advancing grooves are arranged in a noncontinuous helixcut in the screw core in the helical channel of the screw. The pluralityof advancing grooves are dimensioned to receive material therein as thematerial is conveyed through the helical channel, to the outlet port.The longitudinal portion further has a plurality of noncontinuouscross-cut grooves traversing one or more of the advancing grooves. Theplurality of cross-cut grooves includes one or more first cross cutgrooves having a second helix angle (measured relative to a referenceline perpendicular to the longitudinal axis) and one or more secondcross-cut grooves having a third helix angle (measured relative to areference line perpendicular to the longitudinal axis). The first helixangle, the second helix angle and the third helix angle are different.

In one embodiment, the plasticating apparatus includes one or more thirdcross-cut grooves having a fourth helix angle that is different from thefirst helix angle, the second helix angle and the third helix angle.

The present invention also resides in still another screw for aplasticating apparatus. The plasticating apparatus includes a barrelthat has an axial length extending between an inlet port and an outletport. The barrel has an inner wall. The screw has a longitudinal axisand is rotatably supported in the barrel for rotation about thelongitudinal axis. The screw has a core and one or more helical flightsextending along a length of the screw. The helical flight defines ahelix angle relative to a reference line perpendicular to thelongitudinal axis and defines a first helical path of a first helixangle less than ninety degrees. The helical flight defines a helicalchannel. The screw may include a feed section cooperating with the inletport, an intermediate melt section, and/or a metering sectioncooperating with said outlet port. A longitudinal portion of the screw(e.g., in the feed section, the intermediate melt section, and/or themetering section) has a plurality of advancing grooves formed therein.Each of the advancing grooves has one or both ends closed. The advancinggrooves are arranged in a noncontinuous helix cut in the screw core inthe helical channel of the screw. The plurality of advancing grooves aredimensioned to receive material therein as the material is conveyedthrough the helical channel, to the outlet port. The longitudinalportion further has one or more undercut surfaces located radiallyinwardly from the flight surface. The undercut surface has a depth thatvaries in a longitudinal direction parallel to the advancing grooves;and/or in a direction traverse to the longitudinal direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a portion of the surface of a prior artscrew for a plasticating apparatus;

FIG. 2 is a schematic view of a screw for a plasticating apparatus ofthe present invention, shown in a cut away view of a barrel;

FIG. 3 is a schematic view of a portion of the surface of a screw for aplasticating apparatus of the present invention illustrating neutrallyoriented cross-cut grooves on the screw;

FIG. 4A is a schematic view of a portion of the surface of a screw for aplasticating apparatus of the present invention illustrating cross-cutgrooves on the screw oriented in a common direction to the flight of thescrew and each cross-cut groove cutting through one flight;

FIG. 4B is a schematic view of a portion of the surface of a screw for aplasticating apparatus of the present invention illustrating cross-cutgrooves on the screw oriented in a common direction to the flight of thescrew and each cross-cut groove cutting through two flights;

FIG. 5 is a schematic view of a portion of the surface of a screw for aplasticating apparatus of the present invention illustrating acombination of neutrally oriented cross-cut grooves and cross-cutgrooves oriented in a multiple directions;

FIG. 6 is a schematic view of a portion of the surface of a screw for aplasticating apparatus of the present invention illustrating advancinggrooves having varying depths and depth tapers;

FIG. 7A is a cross sectional view of a portion of the surface of thescrew of FIG. 6 taken across line 7A-7A;

FIG. 7B is a cross sectional view of another embodiment of a portion ofthe surface of the screw of FIG. 6 taken across line 7B-7B;

FIG. 7C is a cross sectional view of another embodiment of a portion ofthe surface of the screw of FIG. 6 taken across line 7C-7C;

FIG. 7D is a cross sectional view of another embodiment of a portion ofthe surface of the screw of FIG. 6 taken across line 7D-7D;

FIG. 7E is a cross sectional view of another embodiment of a portion ofthe surface of the screw of FIG. 6 taken across line 7E-7E;

FIG. 8A is a cross sectional view of one of the advancing grooves ofFIG. 6 taken across line 8A-8A showing a decreasing depth taper;

FIG. 8B is a cross sectional view of one of the advancing grooves ofFIG. 6 taken across line 8B-8B showing constant depth taper;

FIG. 8C is a cross sectional view of one of the advancing grooves ofFIG. 6 taken across line 8C-8C showing an increasing depth taper;

FIG. 8D is a cross sectional view of one of the advancing grooves ofFIG. 6 taken across line 8D-8D showing varying depth taper;

FIG. 8E is a cross sectional view of one of the advancing grooves ofFIG. 6 taken across line 8E-8E showing another varying depth taper;

FIG. 8F is a cross sectional view of one of the advancing grooves ofFIG. 6 taken across line 8F-8F showing another varying depth taper;

FIG. 9 is a schematic view of a portion of the surface of a screw for aplasticating apparatus of the present invention illustrating cross-cutgrooves having varying depths and depth tapers;

FIG. 10A is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 10A-10A;

FIG. 10B is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 10B-10B;

FIG. 10C is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 10C-10C;

FIG. 11A is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 11A-11A;

FIG. 11B is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 11B-11B;

FIG. 11C is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 11C-11C;

FIG. 11D is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 11D-11D;

FIG. 11E is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 11E-11E; and

FIG. 11F is a cross sectional view of a portion of the surface of thescrew of FIG. 9 taken across line 11F-11F.

DETAILED DESCRIPTION

Referring to FIG. 2, a plasticating apparatus is generally designated bythe numeral 200. The plasticating apparatus includes a cylindricalbarrel 2 that defines an inner surface 3. The barrel 2 includes an inletport 4 that has a feed hopper 7 connected thereto. The feed hopper 7 andinlet port 4 cooperate to supply one or more solid particulate resinousmaterials and any additives or agents to the barrel 2. The barrel 2includes an outlet port 6 for the discharge of plasticated moltenextrudate to a mold or die (not shown). Heating elements 11 arepositioned outside of the barrel 2 for applying heat to the barrel 2.

As illustrated in FIG. 2, a screw 10 is axially supported for rotationin the barrel 2 along a longitudinal axis A1. The screw 10 extends fromthe inlet port 4 to the outlet port 6. The screw 10 includes a helicalflight 13 radially extending from and winding around a core 12 in afirst direction (e.g., in a right hand threaded direction). The helicalflight 13 includes a radially outermost flight surface 14 (e.g., alsoreferred to as a flight land) which moves in close cooperativeassociation with the inner surface 3 of the barrel 2. The helical flight13 defines a helical channel 18 bounded by flight 13, inner surface 3 ofthe barrel 2 and the surface of the core 12. The depth of the helicalchannel 18 is measured radially from the surface of core 12 to the innersurface 3 of the barrel 2 and is referred to as the root depth RD. Withthe rotation of the screw 10, the helical channel 18 forces a forwardflow in the direction indicated by the arrow 40 of resinous materials.

As shown in FIG. 2, the screw 10 includes a relatively deep root feedsection B for the admission, heating and working of solid resin, atransition section C of reducing root depth to adapt to the reducedvolume of resin due to melting and the elimination of air spaces betweenthe solid particles, and a relatively shallow root metering section Dwherein the resin is a combination of molten and un-melted material. Themetering section D includes a longitudinal portion A. The inlet port 4is typically at the rear-most part of the upstream feed section B andthe outlet port 6 is the forward-most part of the downstream meteringsection D.

As shown in FIG. 3, the longitudinal portion A of the surface of thecore 12 includes a plurality of noncontinuous advancing grooves 30. Theadvancing grooves 30 are arranged to make a forward helical pathway inthe helical channel 18. The advancing grooves 30 are cut into thesurface of core 12. There is a plurality of adjacent grooves 30 perchannel, preferably three as shown, but not limited to only three. Theadvancing grooves 30 are generally elliptically tapered. The advancinggrooves 30 are parallel to and have the same helical pitch and firsthelix angle H1 as the forward helical flight 13. The first helix angleH1 is measured relative to a reference line perpendicular to thelongitudinal axis A1. The advancing grooves 30 facilitate the forwardflow of the resinous material towards the outlet port 6.

As shown in FIG. 3, the longitudinal portion A of the surface of thecore 12 includes a plurality of staggered rows of noncontinuouscross-cut grooves 37N cut into the surface of the core 12 and interceptthrough one flight 13. The axis of each cross-cut groove 37N is parallelto the other cross-cut grooves 37N. The cross-cut grooves 37N areoriented in a neutral direction parallel to the longitudinal axis A1(i.e., at about ninety degrees relative to a reference lineperpendicular to the longitudinal axis). The cross-cut grooves 37Nfacilitate mixing of the resinous material during the transport towardsthe outlet port 6. While the cross-cut grooves 37N are shown anddescribed as intercepting through one flight 13, the present inventionis not limited in this regard as the cross-cut grooves 37N may interceptmore than one flight 13, for example, two flights 13 (e.g., both leadingand trailing flight with respect to the channel 18), as shown in FIG.4B.

As shown in FIG. 4A, the longitudinal portion A of the surface of thecore 12 includes has a plurality of staggered rows of noncontinuouscross-cut grooves 37C cut into the surface of the core 12 and interceptthrough one flight 13. The axis of each cross-cut groove 37C is parallelto the other cross-cut grooves 37C. While the cross-cut grooves 37C areshown and described as being parallel to one another, the cross-cutgrooves 37C may be at different angles to one another. The cross-cutgrooves 37C are oriented in the first direction common to that of thehelical flight (i.e., a right hand threaded direction). The cross-cutgrooves 37C are oriented at a second helix angle H2 that is differentfrom the first helix angle H1 of the advancing grooves 30 and thehelical flight 13. The second helix angle H2 shown in FIG. 4B is greaterthan the first helix angle H1, however in one embodiment, the secondhelix angle H2 may be greater than the first helix angle H1 and lessthan 90 degrees. The cross-cut grooves 37C facilitate mixing of theresinous material during the transport towards the outlet port 6. Whilethe cross-cut grooves 37C are shown and described as interceptingthrough one flight 13, the present invention is not limited in thisregard as the cross-cut grooves 37C may intercept more than one flight13, for example, two flights 13 (e.g., both leading and trailing flightwith respect to the channel 18), as shown in FIG. 4B.

As shown in FIG. 5, the longitudinal portion A of the surface of thecore 12 includes a plurality of the cross-cut grooves 37N and aplurality of the cross-cut grooves 37C cut into the surface of the core12. Each of the plurality of cross-cut grooves 37N and each of theplurality of cross-cut grooves 37C intersect one or both flights 13.Each of the plurality of cross-cut grooves 37N is oriented at thirdhelix angle H3 that is about 90 degrees. Some of the cross-cut grooves37C have a second helix angle H2′ and some of the cross cut grooves 37Chave another second helix angle H2″, wherein the second helix angle H2′is different than the other second helix angle H2″. The second helixangle H2′ and the other second helix angle H2″ are greater than thefirst helix angle H1 of the flight 13. The cross-cut grooves 37N and 37Cfacilitate mixing of the resinous material during the transport towardsthe outlet port 6.

As illustrated in FIG. 6, the advancing grooves 30 have different depthsand different depth tapers along a longitudinal axis of the advancinggroove in a direction of flow Q1 in the advancing groove. The depths aremeasured from the inner surface 3 of the barrel 2 to the radially innermost point of the advancing groove 30. The different depths anddifferent depth tapers of the advancing grooves 30 facilitate mixing ofthe resinous material, for example, by changing velocity distributionsacross the advancing groove 30. As depicted in FIGS. 2 and 4A-6, theadvancing grooves 30 promote flow in the direction indicated by thearrow 40.

For example, as shown in FIG. 7A three adjacent advancing grooves 30have different but uniform depths D1, D2 and D3, respectively. In oneembodiment, D1 and D3 are greater than D2, with the advancing groove 30with the shallow depth D2 being positioned between two advancing grooves30 having greater depths D1 and D3. As shown in FIGS. 7A, 7B and 7Cthere is an undercut surface 66 that is formed (e.g., machine cut into)at a depth D66 which is greater than the land depth LD. Thus, theundercut surface 66 is located radially inwardly from the flight surface14. The undercut surface shown in FIGS. 7A, 7B and 7C has a constantdepth D66.

As shown in FIG. 7B three adjacent advancing grooves 30 have differentbut uniform depths D4, D5 and D6, respectively. In one embodiment, D5and D6 are greater than D4, with the advancing groove 30 with theshallow depth D4 being positioned adjacent to the two adjacent advancinggrooves 30 having greater depths D5 and D6.

As shown in FIG. 7C three adjacent advancing grooves 30 have differentbut uniform depths D7, D8 and D9, respectively. In one embodiment, D7and D8 are greater than D9, with the advancing groove 30 with theshallow depth D9 being positioned adjacent to the two adjacent advancinggrooves 30 having greater depths D7 and D8.

While the undercut surface is shown in FIGS. 7A, 7B and 7C as having aconstant depth D66, the present invention is not limited in this regard.For example, as illustrated in FIG. 7D the undercut surfaces haveundercut groove depths that vary in a direction traverse to thelongitudinal direction along the direction of flow Q1 including: 1) theundercut surfaces 66 adjacent to the flight 13 each have a depth D66; 2)the undercut surface 66′ has a depth D66′ that is less than the depthD66 and greater than the land depth LD; and 3) the undercut surface 66″has a depth D66″ that is greater than the depth D66′. The traversechange in depths of the undercut surface 66, 66′ and 66″ facilitatesmixing of the resinous material, for example, by changing velocitydistributions across the advancing groove 30.

In one embodiment, as shown in FIGS. 6 and 7E the undercut surface has avarying depth in a longitudinal direction along the direction of flowQ1, for example: 1) a portion of the undercut surface 66 has a constantdepth D66; 2) another portion of the undercut surface 66D has anincreasing depth taper along the longitudinal direction of flow Q1 inthe advancing groove 30 wherein a portion of the increasing taper has adepth D66I that is greater than the depth D66; 3) another portion of theundercut surface 66″ has a constant depth D66″ that is greater than thedepth D66 and the depth D66I; 4) another portion of the undercut surface66D has a decreasing depth taper along the longitudinal direction offlow Q1 in the advancing groove 30 wherein a portion of the decreasingdepth taper has a depth of D66D that is less than the depth D66″; and 5)another portion of the undercut surface 66′ has a depth D66′ that isless than the depth D66.

As shown in FIG. 8A the advancing groove 30 has a decreasing depth taperin the first direction (i.e., a longitudinal direction along theadvancing groove in a direction of flow though the advancing groove) asindicated by the arrow Q1. For example, the decreasing depth taper isdefined by a depth D11 that is greater than a depth D10. As shown inFIG. 8B the advancing groove 30 has a constant depth taper in the firstdirection as indicated by the arrow Q1. For example, the constant depthtaper is defined by a uniform depth D12.

As shown in FIG. 8C the advancing groove 30 has an increasing depthtaper in the first direction as indicated by the arrow Q1. For example,the increasing depth taper is defined by a depth D13 that is less than adepth D14.

As shown in FIG. 8D the advancing groove 30 has a varying depth taper inthe first direction as indicated by the arrow Q1. For example, thevarying depth taper is defined by: 1) a section of decreasing depthtaper wherein a depth D15′ is less than a depth D15; 2) a section ofconstant depth D16; 3) and a section of increasing depth taper wherein adepth D17′ is greater than a depth D17.

As shown in FIG. 8E the advancing groove 30 has varying depth taper inthe first direction as indicated by the arrow Q1. For example, thevarying depth taper is defined by: 1) a section of constant depth D18;2) a section of increasing depth taper wherein a depth D19′ is greaterthan a depth D19; 2) a section of constant depth D20; 4) a section ofdecreasing depth taper wherein a depth D21 is less than a depth D21′;and 5) a section of constant depth D18.

As shown in FIG. 8F the advancing groove 30 has a continuously varyingdepth D22, D24 such as a wave or sinusoidal pattern.

While the advancing grooves 30 are shown and described as havingdifferent depths and different depth tapers, the present invention isnot limited in this regard as the cross-cut grooves may also or in thealternative have different depths and different depth tapers. Forexample, as shown in FIGS. 9, 10A, 10B, 10C, 11A, 11B, 11C, 11D, 11E,and 11F, the cross-cut grooves 37N and 37C have different depths anddifferent depth tapers along a longitudinal axis of the cross-cut groovein a direction of flow Q3 in the cross-cut grooves 37C and in thedirection of flow Q2 in the cross-cut grooves 37N. The depths aremeasured from the inner surface 3 of the barrel 2 to the radially innermost point of the cross-cut groove 37N or 37C. The different depths anddifferent depth tapers of the cross-cut grooves 37N and 37C facilitatesmixing of the resinous material, for example, by changing velocitydistributions across the cross-cut grooves 37N and 37C.

As shown in FIGS. 9, 10A and 11A the cross-cut groove 37C has a constantdepth D30 along the longitudinal axis of the cross-cut groove in adirection of flow Q3. As shown in FIGS. 9, 10B and 11B the cross-cutgroove 37C has a constant depth D32 along the longitudinal axis of thecross-cut 37C groove in a direction of flow Q3. As shown in FIGS. 9, 10Cand 11C the cross-cut groove 37N has a constant depth D33 along thelongitudinal axis of the cross-cut groove in a direction of flow Q3. Thedepth D30 is greater than the depth D32 and the depth D32 is greaterthan the depth D33. Thus, the cross-cut grooves 37C and the cross-cutgrooves 37N have different depths relative to other ones of thecross-cut grooves 37C and the cross-cut grooves 37N. While, thecross-cut grooves 37C and the cross-cut grooves 37N are shown anddescribed as having different depths, the present invention is notlimited in this regard as the cross-cut grooves 37C and the cross-cutgrooves 37N may have equal depths or some of the cross-cut grooves 37Cand the cross-cut grooves 37N may have equal depths and other of thecross-cut grooves 37 and the cross-cut grooves 37N may have differentdepths.

As shown in FIGS. 9, 11D, 11E and 11F, the cross-cut grooves 37C and thecross-cut grooves 37N have different depth tapers. As shown in FIGS. 9and 11D, the cross-cut groove 37C has an increasing depth taper alongthe longitudinal axis of the cross-cut groove 37C in a direction of flowQ3 (e.g., the cross-cut groove 37C has a depth D40 proximate one endthereof and a depth D41 proximate another end thereof, wherein the depthD41 is greater than the depth D40). As shown in FIGS. 9 and 11E, thecross-cut groove 37C has a decreasing depth taper along the longitudinalaxis of the cross-cut groove 37C in a direction of flow Q3 (e.g., thecross-cut groove 37C has a depth D44 proximate one end thereof and adepth D43 proximate another end thereof, wherein the depth D44 isgreater than the depth D43). As shown in FIGS. 9 and 11F, the cross-cutgroove 37N has a varying depth taper along the longitudinal axis of thecross-cut groove 37C in a direction of flow Q3. For example: 1) thecross-cut groove 37N has a depth D50 proximate one end thereof and adepth D53 adjacent thereto, wherein the depth D53 is greater than thedepth D50 thereby defining an increasing depth taper; 2) the cross-cutgroove 37N has a constant depth D55 along a central section thereof,wherein the depth D55 is greater than the depth D53; 3) the cross-cutgroove 37N has a depth D52 proximate another end thereof and a depth D53adjacent thereto, wherein the depth D53 is greater than the depth D52thereby defining an decreasing depth taper.

Although the invention has been described with reference to particularembodiments thereof, it will be understood by one of ordinary skill inthe art, upon a reading and understanding of the foregoing disclosurethat numerous variations and alterations to the disclosed embodimentswill fall within the scope of this invention and of the appended claims.

What is claimed is:
 1. A screw for a plasticating apparatus, the screwcomprising: a longitudinal axis, the screw being rotatably supportablein a barrel for rotation about the longitudinal axis, the screw having acore and at least one helical flight extending along a length of thescrew, the helical flight having a radially outermost flight surface,the helical flight extending in a first threaded direction and defininga first helical path of a first helix angle measured relative to areference line perpendicular to the longitudinal axis, the first helixangle being less than ninety degrees; the helical flight defining ahelical channel; and a longitudinal portion of the screw having aplurality of advancing grooves with each advancing groove having atleast one closed-end, the advancing grooves being arranged in anoncontinuous helix cut in the screw core in the helical channel of thescrew, each of the plurality of advancing grooves forming a secondhelical path in the helical channel and being arranged entirely betweenadjacent helical flights and extending substantially parallel to thehelical flights, and the plurality of advancing grooves beingdimensioned to receive material therein as the material is conveyedforward through the helical channel; the longitudinal portion furtherhaving at least one undercut surface located radially inwardly from theradially outermost flight surface, wherein the undercut surface has adepth that varies at least one of: in a longitudinal direction parallelto the plurality of advancing grooves; and in a direction traverse tothe longitudinal direction.
 2. The screw of claim 1, wherein the atleast one undercut surface includes one or more first undercut surfacesadjacent to the helical flight.
 3. The screw of claim 2, wherein: the atleast one undercut surface further includes a second undercut surfacelocated on an opposite side of a first advancing groove, among theadvancing grooves, from one of the first undercut surfaces, and the oneof the first undercut surfaces has a first depth.
 4. The screw of claim3, wherein: the second undercut surface has a second depth that is lessthan the first depth, and the second undercut surface is locatedradially inwardly from the radially outermost flight surface.
 5. Thescrew of claim 4, wherein the at least one undercut surface furtherincludes a third undercut surface located on an opposite side of asecond advancing groove, among the advancing grooves, from the secondundercut surface.
 6. The screw of claim 5, wherein: the third undercutsurface has a third depth that is greater than the second depth, and thethird undercut surface is located radially inwardly from the radiallyoutermost flight surface.
 7. The screw of claim 6, wherein the thirdundercut surface is located on an opposite side of a third advancinggroove, among the advancing grooves, from another one of the firstundercut surfaces.
 8. The screw of claim 1, wherein: the at least oneundercut surface includes a first portion having a first depth, and thefirst depth is substantially constant along the longitudinal direction.9. The screw of claim 8, wherein: the at least one undercut surfacefurther includes a second portion adjacent to the first portion, thesecond portion has an increasing depth taper along the longitudinaldirection, and a portion of the increasing depth taper has a seconddepth that is greater than the first depth.
 10. The screw of claim 9,wherein: the at least one undercut surface further includes a thirdportion adjacent to the second portion, the third portion has a thirddepth, and the third depth is substantially constant along thelongitudinal direction and is greater than the second depth.
 11. Thescrew of claim 10, wherein: the at least one undercut surface furtherincludes a fourth portion adjacent to the third portion, the fourthportion has a decreasing depth taper along the longitudinal direction,and a portion of the decreasing depth taper has a fourth depth that isless than the third depth.
 12. The screw of claim 11, wherein: the atleast one undercut surface further includes a fifth portion adjacent tothe fourth portion, and the fifth portion has a fifth depth that is lessthan the fourth depth.
 13. A screw for a plasticating apparatus, thescrew comprising: a longitudinal axis, the screw being rotatablysupportable in a barrel for rotation about the longitudinal axis, thescrew having a core and at least one helical flight extending along alength of the screw, the helical flight having a radially outermostflight surface, the helical flight extending in a first threadeddirection and defining a first helical path of a first helix anglemeasured relative to a reference line perpendicular to the longitudinalaxis, the first helix angle being less than ninety degrees; the helicalflight defining a helical channel; and a longitudinal portion of thescrew having a plurality of advancing grooves with each advancing groovehaving at least one closed-end, the advancing grooves being arranged ina noncontinuous helix cut in the screw core in the helical channel ofthe screw, each of the plurality of advancing grooves forming a secondhelical path in the helical channel and being arranged entirely betweenadjacent helical flights and extending substantially parallel to thehelical flights, and the plurality of advancing grooves beingdimensioned to receive material therein as the material is conveyedforward through the helical channel; the longitudinal portion furtherhaving at least one undercut surface located radially inwardly from theradially outermost flight surface, wherein the undercut surface has adepth that varies.